643904 has 14 divisors (see below), whose sum is σ = 1277874. Its totient is φ = 321920.

The previous prime is 643889. The next prime is 643919. The reversal of 643904 is 409346.

It is an interprime number because it is at equal distance from previous prime (643889) and next prime (643919).

It can be written as a sum of positive squares in only one way, i.e., 565504 + 78400 = 752^2 + 280^2 .

It is a super-2 number, since 2×643904² = 829224722432, which contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4967 + ... + 5094.

2⁶⁴³⁹⁰⁴ is an apocalyptic number.

643904 is a gapful number since it is divisible by the number (64) formed by its first and last digit.

It is an amenable number.

643904 is a deficient number, since it is larger than the sum of its proper divisors (633970).

643904 is a wasteful number, since it uses less digits than its factorization.

643904 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10073 (or 10063 counting only the distinct ones).

The product of its (nonzero) digits is 2592, while the sum is 26.

The square root of 643904 is about 802.4362903060. The cubic root of 643904 is about 86.3522598630.

The spelling of 643904 in words is "six hundred forty-three thousand, nine hundred four".